Molybdenum silicide bonded boron carbide

ABSTRACT

An abrasion resistant composition comprising between 40 and 60 percent by volume of boron carbide in particulate form, dispersed in a matrix of molybdenum disilicide.

United States Patent Stringer et al.

[451 Nov. 13, 1973 MOLYBDENUM SILICIDE BONDED BORON CARBIDE [22] Filed: Apr. 14, 1972 [21] Appl. No.: 244,242

[30] Foreign Application Priority Data Apr. 14, 1971 Australia 4588 [52] US. Cl 106/43, 51/307, 75/204, 106/55 [51] Int. Cl.. C04b 35/56, C04b 35/58, C04b 35/70 [58] Field of Search 51/307; 75/201, 204; 106/43, 44, 55, 56; 252/516 [56] References Cited UNITED STATES PATENTS 2,582,231 1/1952 Catallo 75/204 X 3,141,768 7/1964 Bard et al. 75/204 3,306,741 2/1967 Lallemant 75/204 3,325,300 6/1967 Wise 106/43 X 2,982,619 5/1961 Long r 106/55 3,343,373 9/1967 Henderson et al.... 258/516 3,353,954 11/1967 Williams 75/201 3,199,993 8/1965 Schrewelius 51/307 X FOREIGN PATENTS OR APPLICATIONS 936,118 9/1963 Great Britain 106/44 OTHER PUBLICATIONS Samsonov et a1. Alloys of the Boron Carbide-Molybdenum Disilicide System" Chem. Abstracts-Jan. 9, 1961- 314i Primary Examiner-Helen M. McCarthy Attorney-Richard C. Sughrue and Gideon Franklin Rothwell et al.

[57] ABSTRACT An abrasion resistant composition comprising between 40 and 60 percent by volume of boron carbide in particulate form, dispersed in a matrix of molybdenum disilicide.

2 Claims, No Drawings MOLYBDENUM SlLlClDE BONDED BORON CARBIDE This invention relates to abrasion resistant composi tions and to articles made from such compositions. The abrasion resistant compositions of this invention find particular application in nozzles for the passage of high velocity streams of, or containing, abrasive materials, for example gas streams containing abrasive particles such as are used in sand-blasting and like operations. They are also useful in grinding wheels, wheel dressing sticks, filament thread guides and the like.

According to this invention there is provided an abrasion resistant composition comprising from 40 to 60 percent by volume of boron carbide in particulate form dispersed in a matrix of molybdenum disilicide.

The preferred compositions of this invention contain from 48 percent to 58 percent by volume of boron carbide. The boron carbide particles preferably range in size from 200 mesh to 400 mesh BSS.

It is known to produce abrasion resistant materials by embedding a hard material in a matrix of a softer material, for example cobalt-bonded tungsten carbide. It is also known that boron carbide is a hard material with a high resistance to abrasion and that this substance can be incorporated into suitable matrices to form an abrasion resistant article. However, we have found that in order to produce a product which has a maximum resistance to abrasion it is important to select the correct matrix material and to ensure that the two substances are present in certain proportions. Our investigations have shown that molybdenum disilicide is the most suitable matrix material, both from the point of view of fabrication (as will be described hereinafter) and for the production of an article which takes greatest advantage of the abrasion resistant properties of boron carbide. The degree of abrasion resistance from such an article is highly dependent on the proportion of the constituents present; thus, articles formed with less than 40 percent boron carbide or more than 60% boron carbide do not perform as well as articles containing the proportions of boron carbide specified above.

The abrasion resistant composition of the invention may be produced by any suitable technique. For example a mixture of boron carbide and molybdenum disilicide, in particulate or powdered form may be hotpressed, i.e. moulded under heat and pressure, to the desired form. However, to ensure that the composite material has maximum mechanical strength and abrasion resistance the material is preferably produced by the technique of reaction pressing which is described in our Australian patent No. 247495 and U.S. Pat. No. 3,353,954. In this method particulate boron carbide in mixed with the finely divided elemental constituents of molybdenum disilicide and the mixture is placed in a mould of the desired shape. Pressure is applied to the material in the mould while the mixture therein is heated to the point where a rapid reaction between the molybdenum and silicon occurs. During the reaction a contraction in the volume of thernixture will occur and it is important to ensure that a uniform pressure is maintained on the mixture during this event.

Generally, it is preferred to have the molybdenum and silicon present in the stoicheiometric proportions necessary to form MoSi However, proportions other than stoicheiometric may be used.

Thus, in accordance with a further aspect of the invention, there is provided a method for producing an abrasion resistant article which comprises forming a mixture containing 40 to 60 percent by volume of boron carbide the balance consisting of finely divided molybdenum and silicon and subjecting the mixture to heat and pressure in a mould such that molybdenum disilicide is formed in situ and a moulded article is formed.

Preferred reaction conditions are a temperature between l,500C. and 1,650C. and a pressure of at least 6,000 lb/sq. in. The maximum pressure is limited only by the bursting strength of the graphite die material.

The invention is illustrated but not limited by the fol lowing examples.

EXAMPLE 1 An airpipe tip for use in a flotation cell for the treatment of lead/zinc ores was produced by mixing 58 percent by volume of 320 mesh boron carbide (B C) with Mo and Si in the stoicheiometric proportions for M0Si The mixture was placed in a suitably shaped die and heated to 1,650C. for 45 minutes under a pressure of 8,000 psi, applied by a plunger. Airpipe tips of this type are subject to considerable wear due to the abrasive action of the ore particles in the surrounding liquid. The tip produced as above showed superior wear resistance to tips made of conventional materials.

EXAMPLE 2 A grit or sand blast nozzle was prepared by mixing 58 percent by volume of B,,C of half 320 mesh, half 500 mesh with Mo and Si in the proportions for MoSi pressing the mixture into a suitably shaped die at 8,000 psi and heating to 1,650C. for 45 minutes while under pressure.

EXAMPLE 3 A grit blast nozzle was prepared by the method of Example 2, using 54 percent by volume of mesh B,,C and a temperature of 1,500C.

EXAMPLE 4 A grit blast nozzle was prepared by the method of Example 2, using 58 percent by volume of 325 mesh B C of high boron content and a temperature of l,650C.

The nozzles of each of Examples 2 to 4 showed no appreciable wear after 400 hours: of use. Conventional bonded tungsten carbide nozzles used under the same conditions were worn out after 40 hours use.

We claim:

11. An abrasion resistant composition consisting essentially of between 40 and 60 percent by volume of boron carbide in particulate form, dispersed in a matrix of molybdenum disilicide.

2. An abrasion resistant composition as defined in claim 1, in which the boron carbide is between 48 and 58 percent of the composition by volume, and the particles of boron carbide are substantially in the size range 200 mesh BSS to 400 mesh BSS.

Patent No. 3,772,042 Dated November 13, 1973 Inventor) Robert Kenneth STRINGER et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

IN THE HEADING:

Assignees name, omitted. Insert the following:

--- Commonwealth Scientific and Industrial Research Organization,

Limestone Avenue, Campbell,

Australian Capital Territory, Commonwealth of Australia Signed and sealed this Lith day of June 197 (SEAL) Attest:

EWARD M.FLETCHER ,JR. I C. MARSHALL DANN AttostingOfficer Commissioner of Patents FORM po'wso (1069) v USCOMM-DC BOB'IG-PGO U.S. GQVERNMENT HUNTING OFHCE I9) 0-386-J3l.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,772,042 Dated November 13, 1973 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

IN THE HEADING:

Assignee's name omitted. Insert the following:

-' Commonwealth Scientific and vIndustrial Research Organization,

Limestone Avenue, Campbell,

Australian Capital Territory, Commonwealth of Australia Signed and sealed this 11th day of June 19714.;

(SEAL) Attest:

EDWARD M.FLETCHER,JR. c. MARSHALL 1mm Attesting Officer Comuisaionor of Patents ORM PO-I 050 (10-69) USCOMM-DC GOING-P69 u.s. aovsnnusnr rnmmm orgies Isl; o-au-au 

2. An abrasion resistant composition as defined in claim 1, in which the boron carbide is between 48 and 58 percent of the composition by volume, and the particles of boron carbide are substantially in the size range 200 mesh BSS to 400 mesh BSS. 